The present invention relates to cutting elements with non-planar interfaces and, more specifically, to cutting elements with non-planar, non-linear interfaces.
Industrial applications such as subterranean drilling, cutting, machining, milling, grinding, and other abrasive operations require tools with high abrasion resistance and impact resistance. In these instances, abrasive compacts designed specifically to provide needed abrasion and impact resistance are deployed. Each abrasive compact typically has an abrasive layer of sintered polycrystalline diamond, wherein the polycrystalline diamond layer is created by subjecting a mass of individual crystals to high pressure and temperature processes or to chemical vapor deposition processes or physical vapor deposition such that intra-crystalline bonding occurs. These abrasive compacts are thus called polycrystalline diamond (PCD) compacts.
Each PCD compact is a coherent, polycrystalline hard composite having a substrate, or mounting layer, and a table made of a superhard abrasive layer. The substrate or mounting layer is typically a metal carbide substrate, while the superhard abrasive layer is made from synthetic or natural diamond, cubic boron nitrite (CBN), wurzite boron nitrite, or combinations thereof. The abrasive layer and the substrate are bonded together using a process known as sintering, or sintered bonding, as known to those skilled in the art. The resulting PCD compact is subsequently mounted to a bit body for use with drilling equipment.
The sintering of the substrate to the polycrystalline material occurs under a temperature that is in excess of 1,300.degree. C. After cooling down from the bonding temperature, the substrate may shrink faster than the polycrystalline material layer due to differences in coefficients of thermal expansion. The differential shrinkage leads to residual shear stresses between the substrate and the PCD layer. As such, thermally-induced stresses are introduced between the substrate and the polycrystalline material, leading to a reduction in the bond strength. In addition, tensile stresses may be introduced in localized regions in an outer cylindrical surface of the substrate and internally in the substrate.
Further, during use, impact forces may release stress in the form of fractures in the compact. As a result, the abrasive layer may spall and/or delaminate, causing a potential separation and loss of the diamond or other superhard material on a cutting surface. These failure modes are likely to lead to instability and, ultimately, a complete failure of the PCD element.
A number of cutter configurations have been developed to overcome the aforementioned problems. To improve the bond between the superhard material and the substrate, certain cutting elements have modified the shape of the superhard material and substrate interface from a traditional planar configuration to a configuration that provides mechanical interlocks between the superhard material and the substrate. Attempts to increase the performance of the cutting elements have also focused on applying a non-planar interface (NPI) geometry such as a ridge to increase the interfacial area between the superhard material and the substrate. The presence of the ridge improves the bonding between the table and the substrate by accommodating a distortion which results from a heating of the cutting assembly during the formation as well as a subsequent bonding of the cutting element onto a carrier. Such distortion results from a difference in coefficients of thermal expansion and moduli of elasticity between the superhard material of the facing table and the less hard material of the substrate.
Yet other NPI cutting elements employ one or more constant cross-sectional grooves or channels on the abrasive layer that communicate with their counterparts on the substrate. However, the use of parallel grooves at the interface as a mechanical interlock is not ideal, because although parallel ridges or similar perturbations create surfaces that have symmetry in cross-sections, they are not symmetrical about a central axis. This in turn requires a correct orientation of the cutter in the drill bit in order to realize the improved mechanical interlocking feature.
Other NPI cutting elements provide sinusoidal-like grooves that run perpendicular to a longitudinal axis of the cutting element. Yet other NPI cutting elements provide grooves that run radially to or in a circular fashion about the longitudinal axis of the cutting element. Further, certain NPI cutting elements position concentric annular rings that expand outwardly from the center of the interface to increase the bonding surface area. The increase in volume of the superhard material at the bonding location increases the wear life of the compact. The resistance to impacts is also improved by providing greater bonding strength between the superhard material and the abrasive layer.
Additionally, other cutting elements use a curved or a domed interface to increase the bonding strength between the superhard material and the substrate. The domed interface, by virtue of its geometry, also increases the volume of the superhard material available for abrasive tasks. However, even with NPI cutting elements, the spalling and delamination of the cutting element still exist. Such failures in the cutting element may necessitate a retooling of the drill bit in the field. When down-time, labor cost and replacement costs are considered, such failures are undesirable, especially in the case of deep-well and off-shore drilling applications.